1. Field of the Invention
The present invention relates to an image forming apparatus configured to form an image with use of developer.
2. Description of the Related Art
Hitherto, a developing device has been installed on an electrophotographic or electrostatic-recording image forming apparatus such as an electrophotographic copying machine, a laser beam printer, and a fax machine. The developing device mainly includes a developing roller (developer carrying member) and a developer amount regulating blade. The developing roller is configured to close an opening of a developer container configured to accommodate developer therein, and is arranged in a partially exposed manner. The developer amount regulating blade is configured to abut against the surface of the developing roller, to thereby keep the amount of the developer conveyed by the developing roller constant.
When the developer adhering on the surface of the developing roller passes through between the surface of the developing roller and the developer amount regulating blade along with the rotation of the developing roller, a surplus amount of the developer is removed from the surface of the developing roller so as to be returned into the developer container. Thus, the developer is formed as a thin layer on the developing roller. Simultaneously, triboelectrification charges are applied to the developer due to the friction with the developer amount regulating blade. Thus, the developer moves from the part of the developing roller, which is exposed from the developer container, onto an electrostatic latent image formed on a surface of a rotating photosensitive drum opposed to the developing roller. Further, the developing device may include a developer supplying member configured to supply the developer to the developer carrying member or a developer collecting member configured to collect the developer on the developer carrying member.
Incidentally, it has become a general system to deliver the developing device as described above from a manufacturer to a user in a form of a removably mountable cartridge. For example, when the developing device does not contain enough developer and thus an image is unprintable, a new developing device in a form that is removably mountable to the image forming apparatus is purchased. The developing device is used by being inserted into the main body of the image forming apparatus. Further, from the viewpoint of preventing developer from leaking out from the developing container during conveyance, the new developing device is often maintained in a state in which the developer is sealed in a developer containing portion inside the developing device until the developing device is delivered to the user from the manufacturer.
That is, the new developing device is in a state in which the surface of the developing roller is not coated with the developer. Therefore, when the new developing device is inserted into the apparatus main body and the developing roller is rotated, an extremely large torque is generated between the developing roller and an abutment member such as the developer amount regulating blade and the developer supplying member. As a result, a significant problem may occur, such as damage on the abutment member or on a driving system for the developing device.
Therefore, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-229333, there has been proposed a method of coating, in advance, the surface of the developing roller before use with a powder coating agent as lubricant.
When such a coating agent is used, however, the following problem may occur.
That is, during an initial operation at the start of the use of the cartridge, if the coating agent applied on the developer carrying member is immediately transferred from the developer carrying member onto the developer supplying member, no lubricant remains on the surface of the developer carrying member. In this case, the frictional force between the developer carrying member and the developer amount regulating blade and the frictional force between the developer carrying member and the developer supplying member increase so that the load necessary for rotating the developer carrying member is increased. In other words, a large load may be applied to the driving system for the developing device.
In order to address this problem, it is necessary to retain the coating agent on the surface of the developer carrying member until the toner is supplied to the developer carrying member so that the surface of the developer carrying member is sufficiently coated with the toner.
Further, as another problem, the coating agent may adversely affect an image during image formation. In other words, when the coating agent remains on the developing roller or inside the developing container even after the start of the use of the cartridge, the coating agent and the developer are present on the surface of the developing roller in a mixed manner. The coating agent is charged (carries charges) when being rubbed against the developer amount regulating blade or the developer supplying member. When an image is formed in this state, the coating agent may adversely affect the image so that there may be a problem in that a defective image such as an image with uneven density or an image with white dots (part in the image without toner (or with very little toner) occurring in a dotted pattern) occurs.
Such a defective image remarkably appears in a case of using, for example, a coating agent that is charged to the same polarity as the developer, and has a high charging ability (is easily charged) as compared to that of the developer. This is because the coating agent having a high charge affects the developer to carry an excessive charge (in other words, the developer is more charged than usual).
In order to prevent the image defects to be caused by the coating agent, it is necessary to execute a sequence of discharging the coating agent outside of the developing container after the start of the use of the developing device.
In order to execute this sequence, it may be effective to cause the developer carrying member to once retain the lubricant (collect the lubricant onto the developer carrying member), and then transfer the lubricant from the developer carrying member onto an image bearing member.